<!doctype html>
<meta charset="utf-8">
<title>window.top: `null`</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id="log"></div>
<script>
async_test(function (t) {
  var iframe = document.createElement('iframe');
  iframe.onload  = t.step_func_done(() => {
    var iWindow = iframe.contentWindow;
    /**
     * `top` should return the top-level browsing context but will return
     * `null` if none exists, such as when any of the BC's ancestor browsing
     *  context container's document elements are disconnected/removed.
     */
    assert_equals(iWindow.top, window);
    document.body.removeChild(iframe);
    assert_equals(iWindow.top, null);
  });

  document.body.appendChild(iframe);
}, '`window.top` is null when browsing context container element removed');

async_test(t => {
  var iframe = document.createElement('iframe');
  var iframe2, removedEl;

  var testFunc = t.step_func(() => {
    var frameWindow = iframe.contentWindow;
    var frame2Window = iframe2.contentWindow;

    assert_equals(frameWindow.top, window);
    assert_equals(frame2Window.top, window);

    iframe.removeEventListener('load', nestFrame);
    iframe2.removeEventListener('load', testFunc);

    removedEl = document.body.removeChild(iframe);

    assert_equals(frameWindow.top, null);
    assert_equals(frame2Window.top, null);

    removedEl.addEventListener('load', t.step_func_done(() => {
      // reattached iframe's browsing context will report window.top
      assert_equals(removedEl.contentWindow.top, window);
      // removed/re-added iframes will have new browsing context / window
      assert_equals(frameWindow.top, null);
      assert_equals(frame2Window.top, null);
    }));

    document.body.appendChild(removedEl);
  });

  var nestFrame = function () {
    iframe2 = iframe.contentDocument.createElement('iframe');
    // Workaround for https://bugzilla.mozilla.org/show_bug.cgi?id=1229707
    iframe2.src = '/common/blank.html';
    iframe2.addEventListener('load', testFunc);
    iframe.contentDocument.body.appendChild(iframe2);
  };

  iframe.addEventListener('load', nestFrame);
  document.body.appendChild(iframe);
}, '`window.top`null when any ancestor browsing context container removed');
</script>
